For the desire of living, acting, &c., blessedly or rightly, is (Def. of the Emotions, i.) the essence of man—that is (III. vii.) , the endeavour made by everyone to preserve his own being.
 Baruch Spinoza, Ethics (1677). copy citation

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Author Baruch Spinoza
Source Ethics
Topic desire essence
Date 1677
Language English
Reference
Note Translated by R. H. M. Elwes
Weblink http://www.gutenberg.org/files/3800/3800-h/3800-h.htm

Context

“No one can desire to be blessed, to act rightly, and to live rightly, without at the same time wishing to be, act, and to live—in other words, to actually exist.
Proof.—The proof of this proposition, or rather the proposition itself, is self—evident, and is also plain from the definition of desire. For the desire of living, acting, &c., blessedly or rightly, is (Def. of the Emotions, i.) the essence of man—that is (III. vii.) , the endeavour made by everyone to preserve his own being. Therefore, no one can desire, &c. Q.E.D.
PROP. XXII. No virtue can be conceived as prior to this endeavour to preserve one's own being.
vii.) ; therefore, if any virtue could be conceived as prior thereto, the essence of a thing would have to be conceived as prior to itself, which is obviously absurd.” source